The principal objective of this project is to obtain scientific information relative to the establishment, survival, function and therapeutic effects of bone marrow grafts in patients with malignancy and various forms of bone marrow failure. More specifically, we plan to study: 1) methods of histocompatibility matching and prediction of graft versus host disease (GVH); 2) methods of preparing individuals for transplantation (i.e., immunosuppression and cytoreductive therapy with drugs and serum products; 3) methods for preventing, detecting and eliminating the presensitized state; 4) the pathogenesis of and recovery from GVH; 5) the immunoincompetent state following marrow grafting; 6) the recurrence of leukemia in donor cells; 7) the therapeutic potential of marrow transplantation in various forms of malignancy and bone marrow failure.